Thin film transistor (TFT) is a switching element commonly used in the display field. A TFT generally includes a gate electrode, a gate insulating layer, an active layer and a source electrode and a drain electrode electrically connected with the active layer, wherein the active layer is usually made from semiconductor materials such as polycrystalline silicon (poly-Si), monocrystalline silicon (mono-Si) and oxide semiconductor. The TFTs may be divided into top-gate TFTs and bottom-gate TFTs according to the relative positional relationship between the gate electrode and the active layer of the TFT.
An array substrate is an important component of a display device. The array substrate generally comprises display regions and non-display regions. A plurality of TFTs arranged in a matrix are generally disposed in the display regions. Each TFT may be configured to control the display state of at least one pixel unit in the display region of the array substrate.